Which of the following tests requires heating prior to observing results?
Benedict's test
Brown paper test
Biuret test
Iodine test
Wendelspecht test
The Correct Answer is A
Choice A reason: Benedict's test is a test for the presence of reducing sugars, such as glucose or maltose, in a solution. The test involves adding Benedict's reagent, which is a blue solution of copper (II) sulfate, sodium carbonate, and sodium citrate, to the solution and heating it in a water bath. If reducing sugars are present, they reduce the copper (II) ions to copper (I) ions, which form a red, orange, or green precipitate of copper (I) oxide. The color and amount of the precipitate indicate the concentration of reducing sugars in the solution. ¹
Choice B reason: Brown paper test is a test for the presence of lipids, such as fats or oils, in a solution. The test involves placing a drop of the solution on a piece of brown paper and letting it dry. If lipids are present, they leave a translucent spot on the paper, which can be seen by holding the paper against a light source. The test is based on the fact that lipids are nonpolar and do not dissolve in water, but can dissolve in organic solvents and stain the paper. ²
Choice C reason: Biuret test is a test for the presence of proteins or peptides in a solution. The test involves adding Biuret reagent, which is a blue solution of copper (II) sulfate and sodium hydroxide, to the solution. If proteins or peptides are present, they form a complex with the copper (II) ions, which changes the color of the solution to violet or pink. The test is based on the fact that proteins and peptides have peptide bonds, which have nitrogen atoms that can coordinate with the copper (II) ions. ³
Choice D reason: Iodine test is a test for the presence of starch in a solution. The test involves adding iodine solution, which is a brown solution of iodine and potassium iodide, to the solution. If starch is present, it forms a complex with the iodine molecules, which changes the color of the solution to blue-black. The test is based on the fact that starch is a polysaccharide that has a helical structure, which can trap the iodine molecules inside. ⁴
Choice E reason: Wendelspecht test is a fictional test that does not exist in reality. It is a made-up name that has no meaning or relevance to the topic of this question. Therefore, it cannot be a valid answer.
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Correct Answer is C
Explanation
Choice A rationale: Starch solution is not a protein solution, but a carbohydrate solution. Starch is a polysaccharide, which is a polymer of glucose molecules. Starch does not contain peptide bonds, which are the bonds that link amino acids in proteins. Therefore, starch solution would not react with the biuret reagent and would not produce a violet color.
Choice B rationale: Olive oil is not a protein solution, but a lipid solution. Olive oil is mainly composed of triglycerides, which are esters of glycerol and fatty acids. Olive oil does not contain peptide bonds, which are the bonds that link amino acids in proteins. Therefore, olive oil would not react with the biuret reagent and would not produce a violet color.
Choice C rationale: Albumin solution is a protein solution. Albumin is a globular protein that is found in blood plasma and egg white. Albumin contains many peptide bonds, which are the bonds that link amino acids in proteins. Therefore, albumin solution would react with the biuret reagent and would produce a violet color.
Choice D rationale: Distilled water is not a protein solution, but a pure solvent. Distilled water is water that has been purified by boiling and condensing. Distilled water does not contain any solutes, such as proteins, carbohydrates, or lipids. Therefore, distilled water would not react with the biuret reagent and would not produce a violet color.
Choice E rationale: Glucose solution is not a protein solution, but a carbohydrate solution. Glucose is a monosaccharide, which is a simple sugar. Glucose does not contain peptide bonds, which are the bonds that link amino acids in proteins. Therefore, glucose solution would not react with the biuret reagent and would not produce a violet color.
Correct Answer is B
Explanation
Choice A rationale: Plant pigments do not produce photon energy, but rather capture it from the sun. Photon energy is the energy carried by particles of light, called photons. Different types of electromagnetic radiation, such as visible light, have different amounts of photon energy depending on their wavelength¹.
Choice B rationale: Plant pigments absorb light energy and use it to initiate photosynthesis. Photosynthesis is the process by which plants convert light energy into chemical energy, stored in the bonds of sugar molecules. Plant pigments are specialized organic molecules, such as chlorophyll and carotenoids, that are found in the chloroplasts of plant cells. They absorb specific wavelengths of light and reflect others, giving plants their characteristic colors²³.
Choice C rationale: Plant pigments do not provide electrons, but rather transfer them to other molecules. Electrons are negatively charged subatomic particles that are involved in chemical reactions. In photosynthesis, plant pigments absorb light energy and use it to split water molecules, releasing electrons, protons, and oxygen. The electrons are then passed along an electron transport chain, generating a proton gradient that drives the synthesis of ATP, an energy molecule. The electrons are also used to reduce NADP+ to NADPH, an electron carrier⁴.
Choice D rationale: Plant pigments do not convert heat to electricity, but rather convert light to chemical energy. Heat and electricity are both forms of energy, but they are not directly involved in photosynthesis. Heat is the kinetic energy of molecules, while electricity is the flow of electrons or electric charge. Plant pigments absorb light energy and use it to drive the chemical reactions of photosynthesis, which produce sugar and oxygen as products⁵.
Choice E rationale: Plant pigments do not reduce NADP, but rather donate electrons to it. Reduction is a chemical reaction in which a molecule gains electrons, while oxidation is a chemical reaction in which a molecule loses electrons. NADP+ is an oxidized form of NADP, which stands for nicotinamide adenine dinucleotide phosphate. It is an electron carrier that accepts electrons from plant pigments in photosystem I, a complex of proteins and pigments in the thylakoid membrane of the chloroplast. The reduced form of NADP is NADPH, which carries electrons and hydrogen for the dark reaction of photosynthesis, which uses CO2 to produce glucose⁶.
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